The invention relates to a hydrostatic axial piston machine having a drum-like cylinder block which is fixedly supported against rotation on a driving shaft or an output shaft and is provided with cylinder boreholes concentrically and parallel to its center line in which axially displaceable pistons are arranged which are supported via spherical heads on a slanting disk which is fixed with respect to the housing and preferably adjustable in its slanting angle, with the cylinder openings opposite the slanting disk sweeping over roughly kidney-shaped low pressure and high pressure control openings of a control body between which reversing regions with additional boreholes are located.
Unwanted pressure and conveyor flow pulsations with a corresponding noise development can occur on the running of the open sides of the cylinder boreholes, or the sides of the cylinder boreholes provided with openings, over the reversing regions located between the low pressure and high pressure control openings, because the open cylinder sides are closed abruptly on running onto the reversing regions and, on running off, are abruptly exposed to a high or low pressure which differs from the pressures prevailing in the cylinder openings.
To alleviate these pressure and conveyor flow pulsations, it is known to connect the run-out and run-in regions of the low pressure and high pressure control openings to the reversing regions by notches or wedge-shaped transitions such as can be seen in FIGS. 13 and 14. It is furthermore known to connect the reversing regions to the low pressure and high pressure control openings by passages such as can be seen in FIGS. 15 and 16.
Since, however, the volumes decisive for the pressure build-up in the cylinder space, namely the dead volume plus the stroke volume, depend on the swivel angle of the slanting disk, the necessary volumes to be supplied for the pressure build-up on the pressure in the high pressure control opening and on the available time interval for the pressure reversing and thus on the speed, an optimum pressure reversing is not possible over the whole operating range with a constant notch between the run-out and run-in regions and the reversing region or with passages connecting the reversing regions to the low pressure and high pressure control openings by passages.
It is generally desired to avoid unwanted pressure and conveyor flow pulsations on the passing of the open cylinder sides over the reversing regions, by the reversing regions being provided with boreholes via which an influencing of the pressure prevailing in the cylinder openings takes place such that a continuous pressure build-up or reduction is assumed in the cylinders on the transition from the low pressure to the high pressure control openings and vice versa. In a hydrostatic machine known from DE 198 18 721 A1, one borehole is respectively disposed in the reversing regions via which a pressure increasing the pressure in the cylinders or a pressure relieving this pressure is applied by pumping and/or loading or load relieving devices. The known hydrostatic machine is, however, complex in that special pumping and/or load relieving devices have to be provided.
It is the object of the invention to provide a hydrostatic axial piston machine of the kind first mentioned in which the additional boreholes located in the reversing region(s), which influence the pressure increase or the pressure drop on the passing of the cylinder openings over the reversing regions, are controlled in dependence on the operation states, namely the pressure, the speed and the swivel angle of the slanting disk. Furthermore, a hydrostatic axial piston machine should be provided in which an unwanted abrupt increase or drop in the pressure in the cylinders should be avoided in a simple and reliable way even with changed operating conditions on the passing of the cylinder openings over the reversing regions.
This object is solved in accordance with the invention by a borehole, which is connected to the high pressure side or the high pressure control opening by a line, opening at least in one reversing region of the control body and by a restrictor controlled by the high pressure being disposed in the line which releases a restrictor opening corresponding to the high pressure in the line. If the open cylinder side sweeps over the borehole, oil under higher pressure flows from this into the cylinder opening so that the pressure in this increased on passing the reversing region and a continuous pressure increase takes place in the cylinder until the open cylinder side runs into the high pressure control opening. Unwanted abrupt pressure increases and changes to the conveyor flow are thereby avoided.
The borehole appropriately opens in a region of the reversing region which is facing the high pressure control opening.
In accordance with a preferred embodiment, it is planned that, at least in a region of the reversing region of the control body facing the low pressure control opening, a borehole opens which is connected to the low pressure control opening by a line and that a restrictor controlled by the high pressure is disposed in the line, which releases a restrictor opening corresponding to the high pressure in the line. This aspect improves the pressure compensation and results in a continuous pressure drop avoiding abrupt pressure changes prior to and during the running of the open cylinder sides into the low pressure control opening.
The two boreholes in the reversing region are appropriately simultaneously covered by the respective cylinder opening on the passing of each of them. The two boreholes appropriately have respectively equal distances to the low pressure and high pressure control openings in the reversing region(s).
Known solutions, for example of the kind described with reference to FIGS. 13 to 16, have the disadvantage that these only ensure an evening of the pressure increase or of the pressure drop on the passing of the open cylinder sides over the reversing regions for a certain operating mode, for example a certain pressure, of the axial piston machine. The solution of the invention is characterized, in contrast to this, by the boreholes in the reversing regions forming restrictor openings by which a pressure approximation takes place via the controlled restrictor which is carried off from the respective high pressure so that the axial piston machine of the invention also ensures a gentle pressure compensation or an adaptation of the pressure on the passing of the open cylinder sides over the reversing regions with different operating modes and in particular with different pressures.
In accordance with an inventive aspect, it is provided that the controlled restrictor consists of a cylindrical borehole in the control body or a cylinder held in the control body in which borehole or which cylinder a control piston loaded by a compression spring is displaceably guided whose side opposite the compression spring is exposed to the high pressure in the high pressure control opening, that lines open into the cylinder borehole or the cylinder at an axial distance to one another, which lines lead to the borehole of the reversing region and to the high pressure control opening or to the low pressure control opening, and that, corresponding to its displacement, the control piston releases differently sized restrictor openings with respect to the line leading to the reversing region. In accordance with this aspect of the invention, a restrictor controlled by the high pressure or the high pressure side is provided with a cross-section restricting the flow which is matched to the respective high pressure and therefore results in an optimum manner in a continuous pressure increase or pressure drop in the cylinder openings passing the reversing regions.
The line of the reversing region opening into the control cylinder can be connected to the line leading to the high pressure control opening or the low pressure control opening respectively by an axial groove with changing cross-section of the control piston, with the changing cross-section being adapted to the respective axial piston machine on the basis of calculations or experience.
In accordance with another embodiment, it is provided that the connection of the control cylinder to the line leading to the reversing region consists of a slot which the control piston releases in a different length in accordance with its displacement on the basis of the high pressure loaded on one side. The released length corresponds to the respective flow cross-section of the controlled restrictor which is matched to the respective axial piston machine.
In accordance with a preferred embodiment, it is provided that the control piston is loaded on one side by at least two mutually encompassing compression springs, of which the spring(s) following the first spring come into use successively in accordance with the displacement of the control piston in the direction of the springs, that is load the control piston with their force. A roughly hyperbolic spring characteristic curve can be provided by this aspect which takes the path of the control piston and the increasing pressure on the high pressure side better into account.
For example, the pressure increases with a constant power and a reduced swivel angle of the slanting disk with a correspondingly reduced volume flow. To take different operating states, for example the pressure change and the change in the volume flow into account in a change of the slanting angle of the slanting disk, a certain control characteristic has to be achieved with respect to the restrictor opening changing its cross-section which takes the special spring characteristic and spring characteristic curve into account. With a change in the slanting angle of the slanting disk, the dead volume in the cylinder between the piston and the control body changes such that changed circumstances result which are taken into account by the restrictor controlled in accordance with the invention. If namely the swivel angle is also changed in addition to the high pressure, a control of the restrictor opening which takes this change into account is also required.
In accordance with another embodiment of the invention, it is provided that the control piston is displaced in the control cylinder by a setting device whose setting path is determined by a control device, for example a computer, in dependence on the high pressure, the speed and the swivel angle of the slanting disk. The values influencing the setting path of the control piston, which result for the respective axial piston machine from the changing high pressure, the changing speed and the changing swivel angle, can be stored in tables (ROM) in the memory of the computer so that the computer adjusts the control piston in accordance with the respectively measured high pressure, the respectively measured speed and the respective swivel angle of the slanting disk.
In accordance with another embodiment of the invention, it is provided that the control piston is formed as a step piston whose annular piston surface and whose disk-shaped piston surface is exposed on the one hand to the high pressure and on the other to a pressure corresponding to the set slanting angle of the slanting disk. The pressure corresponding to the slanting angle of the slanting disk can be carried off, for example, from the pressure in a setting cylinder which adjusts the slanting disk and is proportional to the angle adjustment of the slanting disk.
In accordance with a further aspect of the invention, it is provided that the control piston is formed as a three-stage piston whose piston surfaces formed by the two annular surfaces and the center disk-shaped surface are each exposed to pressures which correspond to the high pressure in the high pressure control opening, to the slanting angle of the slanting disk and to the speed. The pressure corresponding to the speed can be carried off, for example, by an auxiliary pump which is driven by the axial piston machine and which produces a pressure proportional to the speed.
In accordance with a preferred embodiment, it is provided that the boreholes opening into the reversing regions are formed by the boreholes of a constant restrictor. In accordance with the invention, each inlet restrictor has at least two restrictor cross-sections, with the one restrictor being a constant restrictor and being accommodated in the control plate and the other restrictor(s) being accommodated in the vicinity of the control surface of the control body or in the control body itself, with the cross-section(s) of the controllable restrictors being controlled in accordance with the operating states of the axial piston machine such that the pressure build-up and the pressure drop takes the designed course in the controlled cylinder space.
In the described embodiments of the invention, it is possible that a certain volume of pressure oil is taken from the high pressure side, that is the high pressure control openings, which is then lacking in the flowing pressure medium. A lack of pressure medium on the high pressure side can, however, result in turn in unwanted pulsations. For this reason, in accordance with another preferred embodiment of the invention, it is provided that the controlled restrictor is supplied with pressure oil from an external pressure oil source.